Male friend came onto me.

I (19 straight male) have been friends with this guy (15m) from my swimming team for about a year now. We get along really well and meet up and chat quite regularly. I’ve always assumed he was into girls although he never really spoke about them. I noticed that he started complimenting me quite a lot, saying things like “ that hoodie looks really good on you” or “you have an amazing body”. At first i didn’t think anything of it but it started making me a bit uncomfortable especially because he is underage. He recently told me about someone that he had feelings for, and I was pushing him to make a move on this mystery ‘girl’. Turns out he was talking about me and that I was the one he has feelings for. I feel stupid that i didn’t realise he was talking about me this whole time. But i didn’t want to ruin the friendship so i let him down easily saying that i don’t have the same feelings (he has always known I’m straight) but that we can carry on being friends. I’ve tried my best to move past it but he still compliments me a lot, and the compliments are getting more sexual now. I don’t know what else to say to him because i already told him that I don’t have feelings for him. Any advice?